Payment and delivery are not atomically bound

In x402 the payment is verifiably on-chain but the payload is not, so a seller can bill for a response that is empty, stale, or subtly wrong, and nothing links the money to the bytes actually delivered. Solution: commit-reveal fair exchange — the seller publishes a hash commitment of the ciphertext payload to HCS before the 402 quote, the buyer settles on Hedera, the decryption key is revealed, and any mismatch between delivered bytes and the pre-payment commitment is provable by anyone via mirror node. The per-item commit only pencils out at Hedera's fixed sub-cent fee; at EVM gas prices the commitment costs more than the data.